1. Field of the Invention
The present invention relates to a dual-action pressure switch apparatus, which becomes one of turned-on state and turned-off state when the pressure of a pressurized fluid is set in a range, and which becomes the other (that is, a state opposing to the state in the range) of turned-on state and turned-off state when the pressure of the pressurized fluid becomes lower than the lower limit of the range and higher than the upper limit thereof.
2. Description of the Related Art
The dual-action pressure switch apparatus described above is used in, for example, the refrigerating cycle of an automotive air conditioner, to stop the compressor in the refrigerating cycle when the pressure of the refrigerant therein either becomes lower than the lower limit of a range, or higher than the upper limit thereof, thereby to protect the refrigerating cycle from being damaged.
U.S. Pat. Nos. 4,091,249, 4,243,858, 4,220,836, 4,473,729, and 4,296,287 disclose ON/OFF switch apparatuses which are turned on or off by the snap transformation of a snap disk caused by the pressure of a pressurized fluid attaining a certain value.
Japanese Utility Model Disclosures Nos. 57-197146 and 59-82935, U.S. Pat. No. 4,593,166, and Japanese Utility Model Publication No. 62-23009 disclose dual-action pressure switch apparatuses which use a combination of a coil spring and a snap disk or ring. In these dual-action pressure switch apparatuses, the coil spring is first compressed, to turn on a pair of contacts, when the pressure of a pressurized fluid increases and reaches the lower limit of a range, then the snap disk or ring is snap-transformed, to turn off the paired contacts, when the pressure of the pressurized fluid increases and reaches the upper limit thereof.
In a case where vibration is applied to these dual-action pressure switch apparatuses which use the coil springs when the pressure of the pressurized fluid does not reach the lower limit of the range, expansion and contraction of the coil spring caused by the vibration sometimes bring these apparatuses malfunction. In addition, these dual-action pressure switch apparatuses using coil springs tends to frequently repeat turning-on and turning-off at a very narrow point in the neighbors of upper and lower limits of the certain range. This frequent repeat of turning-on and turning-off is called as "chattering", and this produces a noise which tends to cause electronic apparatuses to wrongly operates. Further, the coil spring needs a relatively large working space in its axial direction and this makes the dimension of these dual-action pressure switch apparatuses relatively large in their axial direction. In addition, since it is difficult to accurately determine the length and spring constant of a coil spring when it is manufactured, the spring is therefore provided with a screw type urging force adjusting means. The need to provide such an adjusting means renders the dual-action pressure switch apparatus complicated in its construction, as well as large. In addition, the operation for setting the preload of the spring to a value is extremely bother-some and, moreover, the accuracy of the set preload is not high.
Constructions for eliminating the above-mentioned various drawbacks associated with the use of coil springs in a dual-action pressure switch apparatus are disclosed in Japanese Patent Publication No. 62-37495 and U.S. Pat. No. 4,400,601.
In Japanese Patent Publication No. 62-37495, the dual-action pressure switch apparatus disclosed therein makes use of the resiliency of a pair of switch-contact pieces, instead of a coil spring, and a pair of force transmission members, disposed coaxially and freely slidable in the axial direction to each other, are supported by a partition wall of a housing so as to be slidable in the axial direction, and to transmit the movement of a diaphragm and a snap disk to the switch-contact pieces.
However, it is impossible to accurately determine the value of elasticity of the switch-contact pieces when the contact pieces are manufactured. In addition, the combination of the paired coaxial force transmission members and the partition wall increases the number of parts used in the dual-action pressure switch apparatus and also makes its manufacture and assembly complicated.
In U.S. Pat. No. 4,400,601, the Dual-action pressure switch apparatus disclosed therein makes use of an additional snap disk in place of a coil spring. This pressure switch apparatus has a high-pressure ON/OFF switch, arranged on one side of a partition wall of a housing, and a low pressure ON/OFF switch and a pair of snap disks, for high and low pressures, arranged on the other side of the partition wall. This arrangement needs works for assembling of these components on both sides of the partition wall, thereby causing the assembling works to be troublesome. In addition, the construction of the apparatus is complicated because the components are arranged on both sides of the partition wall.